1. Field of the Invention
This invention relates to a sync crosstalk cancelling circuit which is capable of eliminating crosstalk occurring in multi-track recording (synchronized recording).
2. Description of the Prior Art
In the recording studio, for example, a multi-track recorder with 24 recording channels is used for sync recording and ping-pong recording to record audio signals on each channel, feeding the recorded audio signals into a mixer for mixing, and finally mixing down into two channels, left (L) and right (R), in a master recorder. The master recorder output is input into a disc cutting machine to produce an original disc recording or to dub a multiple number of tapes. The previously mentioned sync recording is the process of playback of a prerecorded channel sound while recording this sound onto another channel at the same time. Ping pong recording is the process of transferring the prerecorded channel sound onto another channel.
FIG. 1 shows a conventional multi-track recorder. In this schematic, 1 is the single molded record/playback head containing the recording head section 1a and the playback head 1b. The recording head section 1a and the playback head section 1b each handle separate tracks on the recording tape and, for example, the recording head section 1a writes the recording signal onto channel "a" and the playback head section 1b reads out the playback signal on channel "b". As shown in FIG. 2, channel "a" and channel "b" are located adjacent to each other on the tape.
The recording amplifier 2 drives the recording head section 1a upon receiving the recording signal. The playback amplifier 3 amplifies the output from the playback head section 1b. The circuit thus operates as follows.
Assume overdub (sync) recording. The audio signal recorded on channel "b" is read by the playback head 1b, amplified by the playback amplifier 3, and input to an audio amplifier (not shown). A speaker (not shown) is driven in accordance to the input signal by the audio amplifier and the playbacked sound output from the speaker. While listening to this sound, another sound is recorded on channel "a." Recording amplifier 2 drives the recording head section 1a and writes the recording signal on channel "a" of the tape.
Now assume ping pong recording (track bouncing). The audio signal recorded on channel "b" is read by the playback head 1b and after proper processing, is input to recording amplifier 2 as the recording signal. In other words, the playback amplifier 3 output (playback output signal) is input to recording amplifier 2 as the recording signal. Recording amplifier 2 drives the recording head section 1a to write the recording signal on channel "a" of the tape. In other words, the content recorded on channel "b" is recorded on channel "a" without any change.
In a multi-track recorder, sync recording and ping pong recording is accomplished using the record/playback head shown in FIG. 1. In this method, the recording head section 1a and the playback head section 1b are molded in one piece and are physically contained in a single head. Consequently, as the recording head section 1a and the playback head section 1b are positioned extremely close together, mutual inductance occurs between the coils. Signal mixing (crosstalk) between the recording head section 1a and the playback head section 1b cannot be avoided. For this reason, a specially constructed head of low crosstalk is generally employed. But accurate playback still cannot be obtained as the recording signal leaks from the coil of the recording section head 1a to the coil of the playback head section 1b thus overlapping on the playback signal. Also, during ping pong recording, there is always the danger of oscillation as a loop circuit is formed and positive feedback will be applied to the signal leaking in.